2000 the Effect of Digital Signal Levels on Analog Channels in a Mixed Signal Multiplex

8/16/2019 2000 the Effect of Digital Signal Levels on Analog Channels in a Mixed Signal Multiplex

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The Effect Of Digital Signal Levels On Analog Channels In A Mixed Signal Multiplex

Marc Ryba and Joseph B. Waltrich

Motorola Broadband Communications Sector

ABSTRACT

In a cable system carrying both analog and

digital signals, the digital signals are typically

run at –10 dB relative to the analog channels.

This is done in order to minimize effects ofdigital third order distortion on the analog

signals. Since distortions produced by digital

signals are noise-like, their effect appears as adecrease in Carrier/Noise ratios in adjacent

analog channels.

Selection of digital power levels is a

compromise between minimizing effects of

analog distortions (i.e.- burst errors) on the

digital channels and maintaining anacceptable noise floor in the analog channels.

This is of particular concern as the industry

moves toward higher density modulationformats such as 256QAM. This paper will

discuss the results of testing to determine

optimum levels of digital signals added to a77 channel analog multiplex.

BACKGROUND

In a typical cable system, analog channels are

located in the lower portion of the spectrum

and digital channels are appended to the highfrequency end. In such a system, theory has

shown that digital third order distortion

produces a noise-like spectrum that extendsinto the lower adjacent analog channels. This

phenomenon is known as Composite

Intermodulation Noise (CIN) and has beendescribed in earlier publications [1], [2]. Theresult is a decrease in the C/N

ratio of the channels at the upper end of the

analog spectrum. The decrease in C/N performance is proportional to the digital

signal power as well as to the number of

digital channels.

Although operating the digital signals atreduced power levels minimizes analog C/N

effects, it makes the digital signals more

susceptible to burst errors resulting from

analog CSO/CTB peaking [3]. Therefore aseries of laboratory tests were conducted to

determine optimum digital/analog ratios for

operation of a mixed signal multiplex.

TEST SYSTEM DESCRIPTION

Test Setup

The system configuration for the tests

consisted of a 77 channel analog multiplex inthe 55-550 MHz range combined with digital

channels above 550 MHz. Tests were

conducted with a total of 32, 16 and 8 digitalchannels. Digital power levels were varied

from zero to –10 dB relative to peak analog

carriers and C/(N+CIN) levels were measuredthroughout the analog spectrum.

A block diagram of the test system is shownin Fig. 1. A 77 channel analog headend was

used to generate the analog signal multiplex.

The analog channels were independently

modulated by separate video test signals. Thedigital multiplex consisted of a maximum of

32 digital signals, received from various

satellites and transcoded to 64QAM via a bank of Motorola IRT1000 Integrated

Receiver/Transcoders. The IRT outputs were

up-converted to RF using MotorolaC6U up-converters and inserted into thecombined signal multiplex starting at 552

MHz. The average digital power levels were

adjusted in 2 dB increments from 0 to –10 dBrelative to peak of analog sync. Regardless of

the number of digital channels, the digital


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signals were always contiguous throughout

the course of the testing.

The distribution system used for the tests

consisted of a 1310 nm laser transmitterdriving a 20 Km fiber optic link with a 1.8

dB in-line optical attenuator followed by an

RF system consisting of a Motorola MB-86SH/G mini-bridger, two Motorola BLE-86S

line extenders and 21 taps. The RF

distribution system was designed with 10 dB

of tilt for 750 MHz spacing. The amplifierswere set up to be driven at their specified

output levels for 77 NTSC carriers plus 200

MHz of compressed data (37/44/37 dBmV for750/550/50 MHz, respectively).

The level of the combined analog/digitalmultiplex was adjusted to provide an input

signal level that is near optimal for the fiber

optic transmitter. With full channel loading,the fiber optic link was monitored for clipping

effects and found to be several dB away from

clipping according to Motorola BCS’s laser

clipping test procedure. A calibrated RF test point is mounted on the front panel of the

laser transmitter module. This point was

monitored via a power meter to provide a

reliable secondary indication of AGC effects

on laser drive level and modulation. As the

channel loading varies, the transmitter’s

microprocessor controlled AGC maintains aconstant drive level to the laser and adjusts

the total input power accordingly.

Analog C/N ratios were measured using a

HP89441 Vector Signal Analyzer. The

analog test signal was monitored after the

second line extender throughout the test. Thistest point provided a signal that was greater

than +25 dBmV per channel for accurate C/N

measurements. A DCT2000 set top terminalwas used to monitor digital signal quality

during the course of the testing. The

monitored digital channel was always locatedat the center of the digital spectrum.

Test Procedure

Unless otherwise specified, all measurements

were performed in accordance with NCTA

recommended practices and procedures.

Analog and digital signal levels were adjusted

to provide a flat spectrum at the input to the

DIGITAL

HEADEND

POWER

METER

FO

TX

FO

RX

DCT2000

ANALOG

HEADEND

VECTOR

SIGNAL

ANALYZER(HP89441)

DISTRIBUTION SYSTEM

MINI-BRIDGER

+ 2 LINE EXTENDERS

FIG. 1 - BLOCK DIAGRAM OF TEST SETUP


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distribution system. The peak analog power

levels were set at +15 dBmV per channel.The average digital power levels were

adjusted from 0 to –10 dBmV per channel

relative to the analog carriers. The totalaverage input power to the laser, after AGC,

was approximately -17 dBm.

All C/(N+CIN) measurements were made at

the first tap after the second line extender. The

HP89441 Vector Signal Analyzer was used to

measure RF analog C/N ratios and digitalEs/No ratios. The peak level for the channel

under test was maintained at a constant +25

dBmV at the input to the HP89441. A tunable bandpass filter, centered on the test channel,

was used for all measurements to eliminate

saturation and distortions at the input to the

test equipment. In-band ripple of the tunablechannel filters did not exceed 0.5 dB in a 6

MHz bandwidth.

A Motorola DCT2000, modified to run

Broadcom QAMLink ™ software, was used tomonitor Bit Error Rate (BER) and ModulationError Ratio (MER) of the digital channel

under observation. The digital test channel

was always located in the center of the digital

spectrum.

TEST RESULTS

Tests with 32 Digital Channels

Test data are shown in Table 1. Table 2 presents the contributions of CIN to the

analog noise floor. Plots of C/(N+CIN) and

C/CIN are shown in Figs. 2 and 3,

respectively. CIN was calculated by treatingit as an additional noise source and

subtracting the effect of Additive WhiteGaussian Noise (AWGN) (i.e. – the systemnoise measured with no digital channels

present) as shown by Equation (1).

CIN=10*Log(100.1*(AWGN+CIN)

– 100.1*AWGN

)

(1)

Where CIN is expressed in dBc and AWGN is

the system noise floor (dBc) with no digitalchannels present.

From Figs. 2 and 3 it is seen that the analogchannels adjacent to the digital multiplex are

affected most severely by the increase in the

analog noise floor due to digital third orderdistortion. This is in accordance with theory

[1].

Although FCC requirements [4] specify aminimum system C/N of 43 dB, most cable

systems are designed to meet more stringent

requirements – typically 49 dB at the end ofthe system. When digital channels are added

to an analog multiplex, the effect of CIN must

be treated as an additional noise source to be

added to the system AWGN. Thereforesystem C/N design goals must include the

effect of CIN as well as AWGN. Table 3

shows the system C/AWGN requirements fora 49 dB C/(N+CIN) design goal. The system

C/AWGN values are calculated as follows:

C/AWGN = -10*Log(10-4.9

– 100.1*CIN

)

(2)

Where C/AWGN is the system

Carrier/AWGN in dB that must be maintainedto meet the required C/(N+CIN) (49 dB in thiscase) and CIN is expressed in dBc.

The blank entry in Table 3 for channel 78 at 0

dB is indicative of a value for which the CINis too large to meet a 49 dB design goal. That

is, equation (2) yields the log of a negative

number. The blank entries in Table 2 at thelowest frequencies are indicative of negligible

CIN values (i.e. – no measurable difference

between CIN and the system noise floor).

In practice, system C/AWGN values greater

than the low 50’s are difficult to achieve. An

inspection of the data in Table 3 shows that ina cable system with a C/(N+CIN) target of 49

dB, the digital channels would have to be

operated at power levels of –6 dB or lower


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relative to the analog channels in order to

maintain desired C/(N+CIN) performance.

Tests With 16 Digital Channels

Test results are shown in Table 4. Table 5

presents the contributions of CIN to the

analog noise floor. Plots of CIN plus systemnoise vs. frequency are shown in Fig. 4. Fig.

5 presents a plot of CIN vs. frequency. The

blank entry in Table 5 indicates a negligible

CIN value. Table 6 shows the C/AWGNvalues required to meet a 49 dB system

C/(N+CIN) design goal.

As is the case with 32 digital channels, a 49

dB system C/(N+CIN) target would require

that the digital signals be operated at –6 dB or

lower relative to the analog carriers. It should be noted, however, that the CIN generated by

16 digital channels at equal power to the

analog signals decreases more rapidly than theCIN for 32 channels in most of the channels

immediately adjacent to the digital spectrum.

This corresponds to theoretical predictions foran octave band decrease in the number of

digital channels [1].

Tests With 8 Digital Channels

Test data and CIN contributions are presentedin Tables 7 and 8, respectively and shown

graphically in Figs. 6 and 7. Table 9 shows

the system C/AWGN requirements needed to

meet a design goal of 49 dB for C/(N+CIN).

From Table 9 it is seen that, in a typical cable

system with a C/(N+CIN) target of 49 dB, thedigital channels could be operated at a power

level of –6 dB or lower relative to the analog

channels. This would depend on how well thesystem AWGN could be controlled.

Since the analog channel most affected by

CIN is the highest channel (i.e. – the loweradjacent channel to the digital spectrum),

maintaining a desired C/(N+CIN) design goal

in this channel should assure that the design

goal would be met in the remainder of the

analog spectrum. Fig. 8 presents plots ofsystem C/AWGN vs. A/D ratio required to

achieve a 49 dB C/(N+CIN) ratio in the worst

case analog channel (EIA channel 78). FromFig. 8 it is seen that an A/D ratio of 6 dB or

greater would be required to operate with a

realistic C/AWGN level. Lower A/D ratiosmay be achievable, depending on the number

of digital channels and the extent to which a

system operator can control system AWGN.

CONCLUSIONS

Test results have shown that digital third orderdistortion may be regarded as an additional

noise source that adds to system AWGN to

produce an increase in the noise floor of the

adjacent analog channels. Test data show thatthis effect is worst in the highest analog

channel and decreases with decreasing analog

channel frequency. Since digital signals areaffected by CSO and CTB peaks, setting

digital signal levels is a compromise between

generation of digital distortion in the analogmultiplex and optimizing digital signal

robustness. To date, it has been a practice to

set levels for 64QAM signals at –10 dBrelative to analog carriers. As 256QAM is

deployed, these levels may have to beincreased. Test data show that a level of –6dB relative to analog signals can be attained

without generating objectionable CIN levels.

The choice of an acceptable operating level is

dependent on the number of digital channelsin the system, the current C/AWGN

performance and the extent to which the

operator is able to control system AWGN.

ACKNOWLEDGEMENTS

The authors wish to express their appreciationto Bill Otto, Chris Lynch and Lenton Jones

for their assistance in conducting the tests.


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REFERENCES

[1] J. Waltrich, “Distortion Produced by

Digital Transmission in a Mixed Analog

and Digital System”, CommunicationsTechnology, April, 1993

[2] J. Hamilton, D. Stoneback, “The Effect ofDigital Carriers on Analog CATV

Distribution Systems’, 1993 NCTA

Technical Papers

[3] O. Sniezko, D. Stoneback, R. Howald,

“Distortion Beat Characteristics and the

Impact on QAM BER Performance”,1999 NCTA Technical Papers

[4] FCC Regulations, Part 76


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EIA Channel 2 16 7 12 32 41 52 63 72 73 74 75 76 77 78

CenterFrequency

(MHz)

57 135 177 207 273 327 393 459 513 519 525 531 537 543 549

A/D Ratio(dB)

System Additive White Gaussian Noise + CIN (dBc)

0 -53.5 -52.8 -52.5 -51.9 -53.1 -52.1 -52.0 -52.5 -49.9 -49.6 -49.7 -50.3 -50.4 -49.8 -48.1

2 -54.1 -53.7 -53.5 -53.4 -54.6 -54.0 -54.0 -54.7 -53.3 -53.0 -53.1 -53.5 -53.7 -53.2 -50.9

4 -54.6 -54.0 -53.7 -54.0 -55.3 -55.0 -55.1 -56.2 -55.2 -54.7 -54.8 -55.4 -55.5 -55.2 -52.7

6 -54.7 -54.3 -54.1 -54.4 -55.7 -55.7 -55.7 -56.7 -56.2 -55.5 -55.7 -56.3 -56.4 -56.2 -54.5

8 -55.1 -54.4 -54.3 -54.5 -55.9 -56.0 -55.9 -56.9 -56.6 -56.0 -56.1 -56.6 -56.9 -56.7 -55.1

10 -55.2 -54.6 -54.4 -54.5 -56.0 -56.0 -56.0 -57.3 -56.8 -56.3 -56.5 -56.9 -57.1 -56.9 -56.2

No Digital -55.2 -54.5 -54.3 -54.6 -56.3 -56.2 -56.4 -57.4 -57.3 -56.8 -56.9 -57.3 -57.6 -57.7 -57.3

Table 1 – System AWGN + CIN for 32 Digital Channels

EIA Channel 2 16 7 12 32 41 52 63 72 73 74 75 76 77 78

CenterFrequency

(MHz)

57 135 177 207 273 327 393 459 513 519 525 531 537 543 549

A/D Ratio

(dB)

CIN (dBc)

0 -58.4 -57.7 -57.2 -55.3 -55.9 -54.2 -54.0 -54.2 -50.8 -50.5 -50.6 -51.3 -51.3 -50.6 -48.7

2 -60.6 -61.4 -61.2 -59.7 -59.5 -58.0 -57.7 -58.0 -55.5 -55.3 -55.4 -55.8 -56.0 -55.1 -52.0

4 -63.5 -63.6 -62.6 -62.5 -62.2 -61.2 -61.0 -62.4 -59.4 -58.9 -59.0 -59.9 -59.7 -58.8 -54.5

6 -64.3 -67.8 -67.6 -68.3 -64.6 -65.3 -64.0 -65.0 -62.7 -61.4 -61.9 -63.2 -62.6 -61.5 -57.7

8 -71.5 -70.8 -71.2 -66.5 -69.5 -65.5 -66.5 -64.9 -63.7 -63.8 -64.9 -65.2 -63.6 -59.1

10 -71.2 -67.8 -69.5 -66.6 -73.7 -66.4 -65.9 -67.1 -67.5 -66.7 -64.6 -62.7

Table 2 – CIN Contribution to Analog Noise Floor for 32 Digital Channels

EIA Channel 2 16 7 12 32 41 52 63 72 73 74 75 76 77 78

CenterFrequency

(MHz)

57 135 177 207 273 327 393 459 513 519 525 531 537 543 549

A/D Ratio(dB)

System C/AWGN (dB)

0 49.5 49.6 49.7 50.2 50.0 50.5 50.7 50.6 53.7 54.3 54.1 52.9 52.8 54.2

2 49.3 49.3 49.3 49.4 49.4 49.6 49.6 49.6 50.1 50.1 50.1 50.0 50.0 50.2 52.0

4 49.2 49.2 49.2 49.2 49.2 49.3 49.3 49.2 49.4 49.5 49.5 49.4 49.4 49.5 50.4

6 49.1 49.1 49.1 49.1 49.1 49.1 49.1 49.1 49.2 49.3 49.2 49.2 49.2 49.2 49.6

8 49.0 49.0 49.0 49.0 49.1 49.0 49.1 49.1 49.1 49.1 49.1 49.1 49.1 49.2 49.4

10 49.0 49.0 49.0 49.0 49.1 49.0 49.1 49.0 49.1 49.1 49.1 49.1 49.1 49.1 49.2

Table 3 – System C/AWGN Required to Meet a 49 dB C/(N+CIN) Design Goal in a System with 32Digital Channels


7/12

Fig. 2 - System AWGN + CIN for 32 Digital Channels

-60.0

-55.0

-50.0

-45.0

0 100 200 300 400 500 600

Center Frequency (MHz)

A W G N + C I N ( d B c ) A/D Ratio = 0 dB

A/D Ratio = 2 dB

A/D Ratio = 4 dB

A/D Ratio = 6 dB

A/D Ratio = 8 dB

A/D Ratio = 10 dB

No Digital

Fig. 3 - CIN Contribution to Analog Noise Floor for 32 Digital Channels

-80.0

-70.0

-60.0

-50.0

-40.0

0 100 200 300 400 500 600

Frequency (MHz)

C I N ( d B c )

A/D Ratio = 0 dB

A/D Ratio = 2 dB

A/D Ratio = 4 dB

A/D Ratio = 6 dB

A/D Ratio = 8 dB

A/D Ratio = 10 dB


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EIA Channel 2 16 7 12 32 41 52 63 72 73 74 75 76 77 78

CenterFrequency

(MHz)

57 135 177 207 273 327 393 459 513 519 525 531 537 543 549

A/D Ratio(dB)


0 -54.0 -53.3 -53.5 -54.0 -54.0 -54.7 -54.7 -55.0 -54.0 -53.0 -53.7 -53.9 -54.0 -53.5 -49.6

2 -54.3 -53.6 -54.0 -55.0 -54.8 -55.4 -55.4 -56.0 -55.0 -55.0 -55.2 -55.5 -56.0 -55.2 -51.7

4 -54.5 -54.0 -54.2 -55.0 -55.4 -56.0 -56.0 -56.6 -56.0 -56.0 -56.0 -56.0 -56.0 -56.1 -53.2

6 -54.8 -54.2 -54.3 -55.0 -55.7 -56.4 -56.4 -56.9 -56.0 -56.0 -56.4 -56.5 -57.0 -56.6 -54.6

8 -54.9 -54.2 -54.6 -56.0 -55.7 -56.5 -56.5 -57.0 -57.0 -56.0 -56.6 -56.8 -57.0 -56.9 -55.4

10 -54.9 -54.4 -54.6 -56.0 -55.7 -56.6 -56.6 -57.2 -57.0 -56.0 -57.1 -56.9 -57.0 -57.1 -56.4

No Digital -55.2 -54.4 -54.7 -56.0 -55.8 -56.8 -56.8 -57.4 -57.0 -57.0 -57.2 -57.2 -58.0 -57.6 -58.3


EIA Channel 2 16 7 12 32 41 52 63 72 73 74 75 76 77 78

CenterFrequency

(MHz)

57 135 177 207 273 327 393 459 513 519 525 531 537 543 549

A/D Ratio

(dB)

CIN (dBc)

0 -60.2 -59.8 -59.7 -58.7 -58.7 -58.9 -58.9 -58.7 -56.3 -55.7 -56.3 -56.6 -56.8 -55.6 -50.2

2 -61.6 -61.3 -62.3 -61.7 -61.7 -61.0 -61.0 -61.6 -59.9 -58.9 -59.5 -60.4 -59.8 -58.9 -52.8

4 -62.8 -64.6 -63.8 -63.4 -66.0 -63.7 -63.7 -64.3 -62.4 -61.4 -62.2 -62.2 -62.5 -61.4 -54.8

6 -65.4 -67.7 -64.9 -64.1 -72.1 -67.0 -67.0 -66.5 -64.6 -63.7 -64.1 -64.8 -65.1 -63.5 -57.0

8 -66.7 -67.7 -71.0 -69.1 -72.1 -68.3 -68.3 -67.6 -67.2 -65.9 -65.5 -67.4 -66.6 -65.2 -58.5

10 -66.7 -71.0 -69.1 -72.1 -70.1 -70.1 -70.7 -70.3 -67.0 -73.5 -68.7 -69.0 -66.7 -60.9


EIA Channel 2 16 7 12 32 41 52 63 72 73 74 75 76 77 78

CenterFrequency

(MHz)

57 135 177 207 273 327 393 459 513 519 525 531 537 543 549

A/D Ratio(dB)

System C/AWGN (dB)

0 49.3 49.4 49.4 49.5 49.5 49.5 49.5 49.5 49.9 50.0 49.9 49.8 49.8 50.1 55.1

2 49.2 49.3 49.2 49.2 49.2 49.3 49.3 49.2 49.4 49.5 49.4 49.3 49.4 49.5 51.4

4 49.2 49.1 49.1 49.2 49.1 49.1 49.1 49.1 49.2 49.3 49.2 49.2 49.2 49.3 50.3

6 49.1 49.1 49.1 49.1 49.0 49.1 49.1 49.1 49.1 49.1 49.1 49.1 49.1 49.2 49.7

8 49.1 49.1 49.0 49.0 49.0 49.1 49.1 49.1 49.1 49.1 49.1 49.1 49.1 49.1 49.5

10 49.1 49.0 49.0 49.0 49.0 49.0 49.0 49.0 49.0 49.1 49.0 49.0 49.0 49.1 49.3



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-60

-55

-50

-45

0 100 200 300 400 500 600

Frequency (MHz)

A W G N + C I N ( d B c ) A/D ratio = 0 dB

A/D Ratio = 2 dB

A/D Ratio = 4 dB

A/D Ratio = 6 dB

A/D Ratio = 8 dB

A/D Ratio = 10 dB

No Digital


-80.0

-70.0

-60.0

-50.0

-40.0

0 100 200 300 400 500 600

Frequency (MHz)

C I N ( d B c )

A/D Ratio = 0 dB

A/D Ratio = 2 dB

A/D Ratio = 4 dB

A/D Ratio = 6 dB

A/D Ratio = 8 dB

A/D Ratio = 10 dB


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EIA Channel 2 16 7 32 41 52 63 72 73 74 75 76 77 78

CenterFrequency

(MHz)

57 135 177 273 327 393 459 513 519 525 531 537 543 549

A/D Ratio(dB)


0 -54.3 -54.6 -53.9 -55.1 -54.4 -55.5 -56.7 -55.8 -55.3 -55.9 -56.2 -56.4 -55.7 -50.5

2 -54.6 -54.8 -54.2 -55.4 -54.7 -55.9 -57.2 -56.5 -55.8 -56.4 -56.9 -57.2 -56.6 -51.9

4 -55.0 -55.1 -54.4 -55.6 -55.0 -56.2 -57.5 -56.8 -56.3 -56.8 -57.2 -57.5 -57.2 -53.5

6 -55.1 -55.3 -54.5 -55.8 -55.1 -56.5 -57.5 -57.1 -56.6 -57.0 -57.5 -57.7 -57.5 -54.7

8 -55.1 -55.3 -54.7 -55.9 -55.2 -56.6 -57.7 -57.2 -56.7 -57.1 -57.7 -57.8 -57.8 -55.8

10 -55.2 -55.3 -54.7 -56.0 -55.4 -56.6 -57.8 -57.5 -56.7 -57.3 -57.7 -58.0 -57.9 -56.5

No Digital -55.4 -55.4 -54.7 -56.1 -55.6 -56.8 -57.8 -57.6 -57.1 -57.5 -58.0 -58.2 -58.4 -58.3


EIA Channel 2 16 7 32 41 52 63 72 73 74 75 76 77 78

CenterFrequency

(MHz)

57 135 177 273 327 393 459 513 519 525 531 537 543 549

A/D Ratio

(dB)

CIN (dBc)

0 -60.8 -62.3 -61.6 -62.0 -60.6 -61.4 -63.2 -60.5 -60.0 -61.0 -60.9 -61.1 -59.0 -51.3

2 -62.3 -63.7 -63.8 -63.7 -62.0 -63.2 -66.1 -63.0 -61.7 -62.9 -63.4 -64.1 -61.3 -53.0

4 -65.6 -66.9 -66.2 -65.2 -63.9 -65.1 -69.3 -64.5 -64.0 -65.1 -64.9 -65.8 -63.4 -55.2

6 -66.9 -71.7 -68.0 -67.6 -64.7 -68.3 -69.3 -66.7 -66.2 -66.6 -67.1 -67.3 -64.8 -57.2

8 -66.9 -71.7 -69.4 -65.8 -70.1 -74.1 -67.8 -67.3 -67.7 -69.5 -68.4 -66.7 -59.4

10 -68.7 -71.7 -72.4 -68.9 -70.1 -73.9 -67.3 -70.8 -69.5 -71.5 -67.5 -61.2


EIA Channel 2 16 7 32 41 52 63 72 73 74 75 76 77 78

CenterFrequency

(MHz)

57 135 177 273 327 393 459 513 519 525 531 537 543 549

A/D Ratio(dB)

System C/AWGN (dB)

0 49.3 49.2 49.2 49.2 49.3 49.3 49.2 49.3 49.4 49.3 49.3 49.3 49.5 52.9

2 49.2 49.1 49.1 49.2 49.2 49.2 49.1 49.2 49.2 49.2 49.2 49.1 49.3 51.2

4 49.1 49.1 49.1 49.1 49.1 49.1 49.0 49.1 49.1 49.1 49.1 49.1 49.2 50.2

6 49.1 49.0 49.1 49.1 49.1 49.1 49.0 49.1 49.1 49.1 49.1 49.1 49.1 49.7

8 49.1 49.0 49.0 49.0 49.1 49.0 49.0 49.1 49.1 49.1 49.0 49.1 49.1 49.4

10 49.0 49.0 49.0 49.0 49.0 49.0 49.0 49.0 49.1 49.0 49.0 49.0 49.1 49.3



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-60

-55

-50

-45

0 100 200 300 400 500 600

Frequency (MHz)

A W G N + C I N ( d B c ) A/D Ratio = 0 dB

A/D Ratio = 2 dB

A/D Ratio = 4 dB

A/D Ratio = 6 dB

A/D Ratio = 8 dB

A/D Ratio = 10 dB

No Digital


-80.0

-70.0

-60.0

-50.0

-40.0

0 100 200 300 400 500 600

Frequency (MHz)

C I N ( d B c )

A/D Ratio = 0 dB

A/D Ratio = 2 dB

A/D Ratio = 4 dB

A/D Ratio = 6 dB

A/D Ratio = 8 dB

A/D Ratio = 10 dB


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Fig. 8 - System C/AWGN Required to Meet 49 dB C/(N+CIN) in Channel 78

48.0

49.0

50.0

51.0

52.0

53.0

54.0

55.0

56.0

0 2 4 6 8 10 12

A/D Ratio (dB)

S y s t e m C / A W G N ( d B )

8 Digital Channels

16 Digital Channels

32 Digital Channels

2000 the Effect of Digital Signal Levels on Analog Channels in a Mixed Signal Multiplex

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